Air Dryer Cartridge with Integrated Check Valve

ABSTRACT

An air dryer cartridge having an outer shell, an inner shell positioned within the outer shell, and a check valve positioned at least partially between the inner and outer shells. The inner and outer shells each have an inlet and an outlet. The outer shell is preferably operable to removably engage an air dryer. The check valve is operable to regulate the rate of flow of fluid through the outlet of the inner shell. Preferably, the check valve also seals between portions of the inner and outer shells and/or is operable to sealingly engage an air dryer.

CROSS-REFERENCE TO RELATED APPLICATIONS

Not applicable.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed to an air dryer cartridge, and morespecifically to an air dryer cartridge having an integrated check valve.

2. Description of Related Art

The pneumatic braking system of a commercial vehicle typically has anair compressor, a governor for controlling the operating cycle of theair compressor, an air dryer and a reservoir for holding pressurized airfor delivery to the pneumatic components, such as the brakes. The aircompressor operates successively in a loading (compressing) mode and anunloading (non-compressing) mode.

When the pressure in the air reservoir falls below a predeterminedminimum pressure, typically about 100 psig, the governor causes the aircompressor to operate in the loading mode to compress air for storage inthe air reservoir. Before storing the air in the air reservoir, thecompressed air from the air compressor passes through an air dryer whichremoves moisture and contaminants therefrom. When the air reservoirreaches the desired pressure, typically about 120 psig, the governorcauses the air compressor to operate in the unloading mode and causesthe purge valve in the air dryer to open to atmosphere.

One type of air dryer includes a removable cartridge that dries thecompressed air as it flows through the cartridge during the loadingmode. During the unloading mode, when the governor causes the purgevalve in the air dryer to open the inlet of the cartridge to exhaust toatmosphere, the air flow direction is reversed and previously driedcompressed air is sent through the cartridge to remove moisture andcontaminants from the cartridge.

A check valve is commonly used to reduce the rate of flow of air throughthe cartridge during the unloading mode in order to more efficientlyremove moisture and contaminants from the desiccant. The check valve isfrequently positioned within a housing of the air dryer, but it may alsobe a part of the air dryer cartridge. One type of air dryer cartridgehas outer and inner shells with a seal positioned between the two todirect air flow through a preferable passage within the cartridge. Theseal is not integrated with a check valve. Typically, air dryercartridges also have two separate gaskets or seals for sealing between abase of the cartridge and an air dryer. These seals are also notintegrated with a check valve.

BRIEF SUMMARY OF THE INVENTION

The present invention is directed toward an air dryer cartridge havingan outer shell, an inner shell positioned within the outer shell, and acheck valve positioned at least partially between the inner and outershells. The inner and outer shells each have an inlet and an outlet. Theouter shell is preferably operable to removably engage an air dryer. Thecheck valve is operable to regulate the rate of flow of fluid throughthe outlet of the inner shell. Incorporating the check valve into theair dryer cartridge permits an operator to replace the check valve byreplacing the entire cartridge without accessing the interior of an airdryer on which the cartridge is installed.

Preferably, the check valve also seals between portions of the inner andouter shells and/or is operable to sealingly engage an air dryer. Thecheck valve is preferably positioned to seal between the inner and outershells and/or sealingly engage an air dryer on which the cartridge isinstalled to reduce complexity of the cartridge and the number of sealsand serviceable items within the cartridge.

The outlet of the inner shell preferably includes a plurality of holesand the check valve preferably has a flap that is moveable between a lowflow rate position, in which it blocks a majority of the holes, and ahigh flow rate position, in which fluid can flow through each of theholes. Preferably, the check valve has a first seal portion coupled withand extending from the flap that seals between portions of the inner andouter shells. The check valve also preferably has a second seal portioncoupled with and extending from the first seal portion that is operableto sealingly engage an air dryer removably engaged by the outer shell.The inlets of the outer and inner shells may be spaced either radiallyinward or radially outward from the outlets of the outer and innershells.

Additional aspects of the invention, together with the advantages andnovel features appurtenant thereto, will be set forth in part in thedescription which follows, and in part will become apparent to thoseskilled in the art upon examination of the following, or may be learnedfrom the practice of the invention. The objects and advantages of theinvention may be realized and attained by means of the instrumentalitiesand combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an air dryer cartridge with anoutside to inside air flow path during a loading mode;

FIG. 2 is a partial cross-sectional view of the cartridge of FIG. 1mounted to a dryer with arrows showing the air flow path during theloading mode;

FIG. 3 is a partial cross-sectional view of the cartridge of FIG. 1mounted to a dryer with arrows showing the air flow path during anunloading mode;

FIG. 4 is a bottom plan view of the cartridge of FIG. 1;

FIG. 5 is a partial cross-sectional view of an alternative embodiment ofair dryer cartridge mounted to a dryer with arrows showing an inside tooutside air flow path during a loading mode;

FIG. 6 is a partial cross-sectional view of the cartridge of FIG. 5mounted to a dryer with arrows showing an air flow path during anunloading mode; and

FIG. 7 is a flow chart of an air dryer system for which the cartridge ofFIG. 1 or FIG. 5 may be used.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

An air dryer cartridge in accordance with one embodiment of the presentinvention is generally shown as 10 in FIG. 1. The cartridge 10 dries andcleans compressed air in an air supply system, such as the system shownin FIG. 7, before the air is routed to a supply reservoir 12, systemreservoirs 13 a and 13 b and/or pneumatic components of the system, suchas brake system 14. The cartridge 10 removably connects to an air dryer16 that receives compressed air from air compressor 18 and routes thecompressed air through the cartridge 10. Preferably, the cartridge 10 isused in the air system of a large motor vehicle such as a bus, truck,semi-tractor, or trailer, but it is within the scope of the inventionfor the cartridge 10 to be used in any type of air system. As discussedin more detail below, the cartridge 10 is operable to both dry and cleanair in a loading mode and be regenerated in an unloading mode duringwhich air flows from a purge reservoir 20 through the cartridge in theopposite direction as the flow of air during the loading mode to removemoisture and contaminants from the cartridge 10.

Referring to FIG. 1, the cartridge 10 includes an outer shell 22, aninner shell 24 positioned within outer shell 22, and a check valve 26positioned partially between the outer shell 22 and inner shell 24. Asdescribed in more detail below, the check valve 26 seals between aportion of outer shell 22 and a portion of inner shell 24 and alsosealingly engages air dryer 16 when the cartridge 10 is removablyinstalled on the air dryer 16 as shown in FIGS. 2 and 3. The check valve26 also regulates the rate of flow of fluid entering the cartridge 10during the unloading mode shown in FIG. 3.

The outer shell 22 includes a cylindrical housing 28 having an open end30 that is partially enclosed by a gasket retainer 32 and base plate 34.The housing 28 includes a side wall 36 integrally joined with a top wall38. A lower end of the side wall 36 adjacent open end 30 is rolled witha peripheral edge of gasket retainer 32 to join the housing 28 andgasket retainer 32. A seal (not shown) may be positioned between theside wall 36 and gasket retainer 32 to prevent air flow between them.The gasket retainer 32 includes a groove 40 in its lower surface thatreceives a gasket 42, which seals between the gasket retainer 32 and airdryer 16, as shown in FIGS. 2 and 3. The gasket retainer 32 includeseight holes 44 a-h (shown in FIG. 4) spaced equidistant from each otherand a center of the cartridge 10 and surrounding a larger central hole46 (shown in FIG. 1).

Base plate 34 is positioned on top of gasket retainer 32. The base plate34 is disk shaped and is sized so that its peripheral edge closely fitswithin the inner surface of side wall 36. The base plate includes eightconcentric holes, two of which are shown as 48 a and 48 b in FIG. 1,each aligned with the holes 44 a-h of gasket retainer 32 and surroundinga larger central hole 50 that is smaller than and aligned with thecentral hole 46 of gasket retainer 32. The aligned holes 44 a-h and 48a-b of gasket retainer 32 and base plate 34, respectively, incombination form an inlet of the outer shell 22. The aligned holes 46and 50 of the gasket retainer 32 and base plate 34, respectively, forman outlet of the outer shell 22. Base plate 34 has a cylindrical,threaded surface 52 that surrounds opening 50 and engages a threadedsurface 53 (FIG. 2) on air dryer 16 when the cartridge 10 is installedon the air dryer 16 as shown in FIGS. 2 and 3.

Inner shell 24 includes a cylindrical side wall 54 that is joined withan integral bottom wall 56 at one end and has an open end 58 oppositebottom wall 56. A cylindrical inner wall 60 is integral with and extendsupward from bottom wall 56. Inner wall 60 is concentric with and has asmaller diameter than side wall 54. Bottom wall 56 includes a pluralityof holes 62 positioned between the side wall 54 and inner wall 60 thatin combination form an inlet of the inner shell 24. Bottom wall 56 alsoincludes a plurality of holes 64 surrounded by the inner wall 60 that incombination form an outlet of the inner shell 24. The holes 64 include acentral hole 64 a and a plurality of holes 64 b spaced radially outwardfrom the central hole 64 a. The inlets of outer shell 22 and inner shell24 are spaced radially outward from the outlets of outer shell 22 andinner shell 24. Bottom wall 56 is spaced a distance from base plate 34to create a ring-shaped chamber 65 between them.

A ring-shaped pre-filter 66 is supported by bottom wall 56 and ispositioned between side wall 54 and inner wall 60. Although pre-filter66 occupies the entire space between bottom wall 56 and the coalescingfilter 68 described below, only a portion of pre-filter 66 is shown inFIG. 1 so that holes 62 are visible. Pre-filter 66 filters relativelylarge particles of contaminants from the air passing through it. Asecond ring-shaped coalescing filter(s) 68 is supported by filter 66 andis positioned between side wall 54 and inner wall 60. Coalescing filter68 is designed to collect and remove oil aerosols from the compressedair. A third ring-shaped filter pad 70 is supported by filter 68 and ispositioned between side wall 54 and inner wall 60. Filter pad 70 alsoremoves contaminants from the air passing through it. Desiccant beads 72fill the inner shell 24 between side wall 54 and inner wall 60 andwithin inner wall 60. Only a small number of desiccant beads 72 areshown in the drawings for clarity. The desiccant beads 72 absorbmoisture from air that enters the inner shell 24 through holes 62 as iswell known in the art. Filters 66, 68, and 70 prevent desiccant beads 72from exiting inner shell 24 through holes 62. Another disk-shaped finefilter 74 is supported by bottom wall 56 and surrounded by inner wall60. Although fine filter 74 covers all of holes 64, only a portion offine filter 74 is shown in FIG. 1 so that holes 64 are visible. Finefilter 74 removes contaminants from air passing through it and preventsfine particles (dust) from exiting inner shell 24 through holes 64.

A load plate 76 and spring 78 are positioned between the desiccant beads72 and top wall 38 of housing 28 to reduce gaps between the desiccantbeads 72 and improve the performance of the beads 72. The load plate 76includes a cylindrical side wall 80 that is slidably received by theside wall 54 of inner shell 24 and a top wall 82 integral with side wall80 and spaced a distance from top wall 38 of housing 28. A springretainer 84 is integral with and extends upward from top wall 82 towardthe top wall 38 of housing 28. The spring retainer 84 includesconcentric circular walls spaced a distance to define a groove forreceiving a portion of spring 78 therebetween. Spring 78 is a coilspring positioned between the top wall 38 of housing 28 and top wall 82of load plate 76 that forces load plate 76 downward to exert pressure ondesiccant beads 72.

Check valve 26 includes a generally circular base 86 with a peripheryforming a first seal portion 88 that seals between the base plate 34 ofouter shell 22 and bottom wall 56 of inner shell 24. The base 86includes a middle portion 90 integral with and extending radially inwardfrom first seal portion 88. The middle portion 90 is slightly thinnerthan the first seal portion 88 to create a groove between the first sealportion 88 and a second seal portion 92 that is integral with andextends downward from middle portion 90. Five flaps 94 a-e (shown inFIG. 4) are integral with and extend radially inward from the middleportion 90. While five flaps are shown in FIG. 4, it is within the scopeof the invention for the check valve 26 to have any number of flaps. Thesecond seal portion 92 includes a cylindrical section 92 a extendinggenerally perpendicular downward from the flaps 94 a-e and a tapered end92 b with a triangular cross-section extending downward from thecylindrical section 92 a. The tapered end 92 b extends outward from thecylindrical section 92 a and is operable to fit tightly against an innercylindrical surface 96 of dryer 16, as shown in FIG. 2, for sealinglyengaging dryer 16 and preventing air from flowing between the dryer 16and second seal portion 92. The second seal portion 92 is generallyconcentric with and spaced apart from the cylindrical, threaded surface52 of base plate 34. A cylindrical protrusion 98 of dryer 16 thatdefines inner surface 96 and contains threads 53 on its outer surface ispositioned between the cylindrical, threaded surface 52 of base plate 34and second seal portion 92 when cartridge 10 is installed on dryer 16.The protrusion 98 also abuts the first seal portion 88 and middleportion 90 and fits within the groove between the first seal portion 88and second seal portion 92.

The flaps 94 a-e of check valve 26 are operable to regulate the rate offlow of fluid through the holes 64 comprising the outlet of the innershell 24. Referring to FIG. 2, when air enters the cartridge 10 in aloading mode through holes 44 a-e of outer shell 22 and exits throughholes 64 of inner shell 24, the air causes the flaps 94 a-e to flex awayfrom the bottom wall 56 of inner shell 24. When the flaps 94 a-e are inthis flexed, high flow rate position, the flaps 94 a-e do not coverholes 64 so that air is operable to flow through the holes 64 and out ofthe cartridge 10 at a relatively high flow rate. A relatively high flowrate is desirable in the loading mode so that the air compressor 18(FIG. 7) can quickly pressurize the air system. Referring to FIG. 3,when air enters the cartridge 10 in an unloading mode through the outletof the outer shell 22 defined by holes 46 and 50, the flaps 94 a-e arepressed against the bottom wall 56 of inner shell 24. When the flaps 94a-e are in this low flow rate position, the flaps 94 a-e cover holes 64b leaving hole 64 a as the only hole 64 through which air can flow intothe inner shell 24. Because air can only flow through hole 64 a when theflaps 94 a-e are in this position, air flows through the cartridge 10 ata lower flow rate in the unloading mode than when in the loading mode. Alower flow rate is desirable in the unloading mode to maximize theremoval of moisture and contaminants from the desiccant beads 72.

Referring now to FIGS. 5 and 6, a second embodiment of air dryercartridge in accordance with the present invention is shown generally as100. Cartridge 100 may be substituted for the cartridge 10 shown in FIG.7 to dry and clean compressed air in the air supply system. Likecartridge 10, cartridge 100 is operable to both dry and clean air in aloading mode and be recharged in an unloading mode during which airflows from a purge reservoir 20 through the cartridge in the oppositedirection as the flow of air during the loading mode to remove moistureand contaminants from the cartridge 100.

Referring to FIGS. 5 and 6, the cartridge 100 includes an outer shell102, an inner shell 104 positioned within outer shell 102, and a checkvalve 106 positioned partially between the outer shell 102 and innershell 104. As described in more detail below, the check valve 106 sealsbetween a portion of outer shell 102 and a portion of inner shell 104and also sealingly engages air dryer 16 when the cartridge 100 isremovably installed on the air dryer 16 as shown in FIGS. 5 and 6. Thecheck valve 106 also regulates the rate of flow of fluid entering thecartridge 100 during the unloading mode shown in FIG. 6.

The outer shell 102 includes a cylindrical housing 108 having an openend 110 that is partially enclosed by a gasket retainer 112 and baseplate 114. The housing 108 includes a side wall 116 integrally joinedwith a top wall (not shown) in a similar manner as the housing 28 shownin FIG. 1. A lower end of the side wall 116 adjacent open end 110 isrolled with a peripheral edge of gasket retainer 112 to join the housing108 and gasket retainer 112. A seal (not shown) may be positionedbetween the side wall 116 and gasket retainer 112 to prevent air flowbetween them. The gasket retainer 112 includes a groove 118 in its lowersurface that receives a gasket 120, which seals between the gasketretainer 112 and air dryer 16, as shown in FIGS. 5 and 6. The gasketretainer 112 includes eight holes, one of which is shown as 122, spacedequidistant from each other and a center of the cartridge 100 andsurrounding a larger central hole 124. The holes 122 are similar to theholes 44 a-h of cartridge 10 shown in FIG. 4.

Base plate 114 is positioned on top of gasket retainer 112. The baseplate 114 is disk shaped and is sized so that its peripheral edgeclosely fits within the inner surface of side wall 116. The base plate114 includes eight concentric holes, one of which is shown as 126, eachaligned with the holes 122 of gasket retainer 112 and surrounding alarger central hole 128 that is smaller than and aligned with thecentral hole 124 of gasket retainer 112. The aligned holes 122 and 126of gasket retainer 112 and base plate 114, respectively, in combinationform an outlet of the outer shell 102. The aligned holes 124 and 128 ofthe gasket retainer 112 and base plate 114, respectively, form an inletof the outer shell 102. Base plate 114 has a cylindrical, threadedsurface 130 that surrounds opening 128 and engages a threaded surface 53on air dryer 16 when the cartridge 100 is installed on the air dryer 16as shown in FIGS. 5 and 6.

Inner shell 104 includes a cylindrical side wall 132 that is joined withan integral bottom wall 134 at one end and has an open end (not shown)opposite bottom wall 134 similar to inner shell 24 shown in FIG. 1.Bottom wall 134 includes a peripheral angled section 134 a integral withand extending downward from side wall 132 and a central horizontalsection 134 b integral with angled section 134 a. A step 136 includingsubstantially vertical and horizontal surfaces extends upward frombottom wall section 134 b. A cylindrical inner wall 138 is integral withand extends upward from step 136. Inner wall 138 is concentric with andhas a smaller diameter than side wall 132. Central section 134 b ofbottom wall 134 includes a plurality of holes 140 and 142 positionedbetween the side wall 132 and inner wall 138 that in combination form anoutlet of the inner shell 104. Holes 140 have a larger diameter thanholes 142. Preferably, there are four holes 142 evenly spaced from eachother and having a diameter of approximately 0.035 inches. Preferably,there are a plurality of holes 140 for allowing air to flow at arelatively high flow rate out of the inner shell 104. Central section134 b also includes a plurality of holes 144 surrounded by the innerwall 138 that in combination form an inlet of the inner shell 104. Theoutlets of outer shell 102 and inner shell 104 are spaced radiallyoutward from the inlets of outer shell 102 and inner shell 104. Bottomwall 134 is spaced a distance from base plate 114 to create a chamber146 between them.

A circular pre-filter 148 is supported by bottom wall 134 and issurrounded by inner wall 138. Pre-filter 148 preferably performs thesame functions as the pre-filter 66 shown in FIG. 1. A second circularcoalescing filter 150 is supported by filter 148 and is surrounded byinner wall 138. Coalescing filter 150 preferably performs the samefunctions as the coalescing filter 68 shown in FIG. 1. A third circularfilter pad 152 is supported by filter 150 and is surrounded by innerwall 138. Filter pad 152 preferably performs the same functions as thefilter pad 70 shown in FIG. 1. Desiccant beads 154 fill the inner shell104 between side wall 132 and inner wall 138 and within inner wall 138.Only a small number of desiccant beads 154 are shown in the drawings forclarity. The desiccant beads 154 remove moisture and contaminants fromair that enters the inner shell 104 through holes 144 as is well knownin the art. Filters 148, 150, and 152 prevent desiccant beads 154 fromexiting inner shell 104 through holes 144. Another ring-shaped finefilter 156 is supported by bottom wall 134 above holes 140 and 142. Finefilter 156 preferably performs the same functions as the fine filter 74shown in FIG. 1 and prevents desiccant beads 154 from exiting innershell 104 through holes 140.

The cartridge 100 preferably has a load plate (not shown) and spring(not shown) that are similar to the load plate 76 and spring 78 ofcartridge 10 described above and shown in FIG. 1 to reduce gaps betweenthe desiccant beads 154 and improve the performance of the beads 154.

Check valve 106 includes a generally circular base 158 that forms afirst seal portion sealing between the base plate 114 of outer shell 102and bottom wall 134 of inner shell 104. The peripheral edge of the base158 forms a flap 160 extending radially outward from the first sealportion. A groove 162 in the base 158 receives a correspondingprotrusion of bottom wall 134 for aligning the check valve 106. A secondseal portion 164 is integral with and extends downward from base 158.The second seal portion 164 includes a cylindrical section extendinggenerally perpendicular downward from the base 158 and a tapered end 166with a triangular cross-section extending downward from the cylindricalsection. The tapered end 166 extends outward from the cylindricalsection and is operable to fit tightly against an inner cylindricalsurface 96 of dryer 16, as shown in FIG. 5, for sealingly engaging dryer16 and preventing air from flowing between the dryer 16 and second sealportion 164. The second seal portion 164 is generally concentric withand spaced apart from the cylindrical, threaded surface 130 of baseplate 114. Cylindrical protrusion 98 of dryer 16 that defines innersurface 96 and contains threads 53 on its outer surface is positionedbetween the cylindrical, threaded surface 130 of base plate 114 andsecond seal portion 164 when cartridge 100 is installed on dryer 16. Theprotrusion 98 also abuts the base 158.

The flap 160 of check valve 106 is operable to regulate the rate of flowof fluid through the holes 140 comprising a portion of the outlet of theinner shell 104. Referring to FIG. 5, when air enters the cartridge 100in a loading mode through hole 128 of outer shell 102 and holes 144 ofinner shell 104 and exits through holes 140 and 142 of inner shell 104,the air causes the flap 160 to flex away from the bottom wall 134 ofinner shell 104. When the flap 160 is in this flexed, high flow rateposition, the flap 160 is positioned away from the holes 140 so that airis operable to flow through the holes 140 and out of the cartridge 100at a relatively high flow rate. Referring to FIG. 6, when air enters thecartridge 100 in an unloading mode through the outlet of the outer shell102 defined by holes 122 and 126, the air presses flap 160 into a lowflow rate position against bottom wall 134 where it covers holes 140.Thus, in the unloading mode air is blocked from flowing through holes140 and can only flow into inner shell 104 through holes 142. Becausethere are only four holes 142 having a relatively small diameter, therate of flow of air into inner shell 104 during the unloading mode isless than the rate of flow of air through the cartridge 100 during theloading mode.

In operation, referring to FIG. 7, when the air system is operating in aloading mode, air compressor 18 compresses air that flows into air dryer16. The air passes from air dryer 16 into either air dryer cartridge 10or air dryer cartridge 100 (shown in FIG. 5) to dry and clean the air asdescribed above. The air flows out of air dryer cartridge 10 back intoair dryer 16. The air dryer 16 has two outlets, one for supplying air topurge reservoir 20 and another for supplying air to supply reservoir 12.The air dryer 16 also has an outlet one-way check valve 170 that the airpasses through before entering supply reservoir 12. Supply reservoir 12supplies air to system reservoirs 13 a and 13 b, which store thepressurized air until it is needed to operate components of brake system14. Each of the system reservoirs 13 a and 13 b has an inlet one-waycheck valve 171 a and 171 b, respectively, that prevents air in thesystem reservoirs 13 a and 13 b from flowing back into the supplyreservoir 12. During the loading mode, the air pressure in purgereservoir 20 and supply reservoir 12 is approximately equal. Governor172 is fluidly coupled with supply reservoir 12 to sense when the airpressure reaches a cut off level. When the air pressure within supplyreservoir 12 reaches a cut off level, governor 172 operates anunloader(s) (not shown) within the air compressor 18 which shuts off aircompressor 18. The governor 172 also opens a purge valve (not shown) ofair dryer 16 which causes air within the air dryer 16 to exhaust fromthe air dryer 16 to the atmosphere. When air compressor 18 shuts off,the air system is in an unloading mode for removing moisture andcontaminants from air dryer cartridge 10. In the unloading mode, airflows from the purge reservoir 20 through air dryer 16 and air dryercartridge 10 in the reverse direction as the air flow during the loadingmode. The air removes moisture and contaminants from the air dryercartridge 10 and exhausts from the air dryer 16 to the atmosphere.During the unloading mode, check valve 170 prevents air from flowing outof supply reservoir 12 back into air dryer 16. In the unloading mode,the air flows in reverse through air dryer cartridge 10 at a lower flowrate than in the loading mode, as described above. It is within thescope of the invention for cartridges 10 and 100 to be used in differenttypes of systems then the one shown in FIG. 7 and described herein. Forexample, the purge reservoir 20 may be incorporated within the air dryer16, and the purge reservoir 20 may be connected in series to the supplyreservoir 12 instead of being connected in parallel to the supplyreservoir 12 as shown in FIG. 7. Alternatively, purge reservoir 20,check valve 170, and check valve 171 b may be omitted so that air fromsystem reservoir 13 b flows in reverse through the air dryer cartridge10 during the unloading mode. In this embodiment of air system, thesystem reservoir 13 b has a pressure controlled check valve (not shown)and the air dryer 16 includes a valve (not shown) at its outlet thatregulates the amount of air from system reservoir 13 b that flows inreverse through the air dryer cartridge 10.

From the foregoing it will be seen that this invention is one welladapted to attain all ends and objectives herein-above set forth,together with the other advantages which are obvious and which areinherent to the invention.

Since many possible embodiments may be made of the invention withoutdeparting from the scope thereof, it is to be understood that allmatters herein set forth or shown in the accompanying drawings are to beinterpreted as illustrative, and not in a limiting sense.

While specific embodiments have been shown and discussed, variousmodifications may of course be made, and the invention is not limited tothe specific forms or arrangement of parts and steps described herein,except insofar as such limitations are included in the following claims.Further, it will be understood that certain features and subcombinationsare of utility and may be employed without reference to other featuresand subcombinations. This is contemplated by and is within the scope ofthe claims.

What is claimed and desired to be secured by Letters Patent is asfollows:
 1. An air dryer cartridge, comprising: an outer shellcomprising an inlet and an outlet; an inner shell positioned within saidouter shell and comprising an inlet and an outlet; and a check valvepositioned at least partially between said outer shell and said innershell and sealing between a portion of said outer shell and a portion ofsaid inner shell, wherein said check valve is operable to regulate therate of flow of fluid through said outlet of said inner shell.
 2. Theair dryer cartridge of claim 1, wherein said outlet of said inner shellcomprises a plurality of holes, wherein said check valve comprises atleast one flap moveable between a low flow rate position, in which saidflap restricts the rate of flow of fluid through at least a portion ofsaid holes, and a high flow rate position.
 3. The air dryer cartridge ofclaim 2, wherein said check valve comprises a plurality of flapsmoveable between said low flow rate position, in which said flaps blockfluid from flowing through a majority of said holes, and said high flowrate position, in which fluid can flow through each of said holes. 4.The air dryer cartridge of claim 3, wherein said check valve comprises afirst seal portion coupled with and extending radially outward from saidflaps, wherein said first seal portion seals between a portion of saidouter shell and a portion of said inner shell.
 5. The air dryercartridge of claim 4, wherein said outer shell is operable to removablyengage an air dryer, wherein said check valve comprises a second sealportion coupled with and extending from said first seal portion, whereinsaid second seal portion is operable to sealingly engage said air dryer.6. The air dryer cartridge of claim 5, wherein said inlet of said outershell and said inlet of said inner shell are spaced radially outwardfrom said outlet of said outer shell and said outlet of said innershell.
 7. The air dryer cartridge of claim 2, wherein said flap blocksfluid from flowing through a majority of said holes when in said lowflow rate position, and wherein fluid can flow through each of saidholes when said flap is in said high flow rate position.
 8. The airdryer cartridge of claim 2, wherein said check valve comprises a firstseal portion coupled with and extending radially inward from said flap,wherein said first seal portion seals between a portion of said outershell and a portion of said inner shell.
 9. The air dryer cartridge ofclaim 8, wherein said outer shell is operable to removably engage an airdryer, wherein said check valve comprises a second seal portion coupledwith said first seal portion and extending from said first seal portion,wherein said second seal portion is operable to sealingly engage saidair dryer.
 10. The air dryer cartridge of claim 9, wherein said inlet ofsaid outer shell and said inlet of said inner shell are spaced radiallyinward from said outlet of said outer shell and said outlet of saidinner shell.
 11. The air dryer cartridge of claim 1, further comprisingdesiccant positioned within said inner shell.
 12. An air dryercartridge, comprising: an outer shell comprising an inlet and an outlet,wherein said outer shell is operable to removably engage an air dryer;an inner shell positioned within said outer shell and comprising aninlet and an outlet; and a check valve positioned at least partiallybetween said outer shell and said inner shell, wherein said check valveis operable to regulate the rate of flow of fluid through said outlet ofsaid inner shell, and wherein said check valve is operable to sealinglyengage said air dryer.
 13. The air dryer cartridge of claim 12, whereinsaid outlet of said inner shell comprises a plurality of holes, whereinsaid check valve comprises at least one flap moveable between a low flowrate position, in which said flap restricts the rate of flow of fluidthrough at least a portion of said holes, and a high flow rate position.14. The air dryer cartridge of claim 13, wherein said check valvecomprises a seal portion coupled with and extending from said flap,wherein said seal portion is operable to sealingly engage said airdryer.
 15. The air dryer cartridge of claim 14, wherein said outer shellcomprises a cylindrical surface, wherein said seal portion is generallyconcentric with and spaced apart from said cylindrical surface, andwherein said cylindrical surface is operable to engage a portion of saidair dryer such that said portion of said air dryer is positioned betweensaid cylindrical surface and said seal portion.
 16. The air dryercartridge of claim 15, wherein said seal portion comprises a cylindricalsection extending generally perpendicular from said flap, and a taperedend extending from said cylindrical section.
 17. An air dryer cartridge,comprising: an outer shell comprising an inlet and an outlet, whereinsaid outer shell is operable to removably engage an air dryer; an innershell positioned within said outer shell and comprising an inlet and anoutlet; and a check valve positioned at least partially between saidouter shell and said inner shell and sealing between a portion of saidouter shell and a portion of said inner shell, wherein said check valveis operable to regulate the rate of flow of fluid through said outlet ofsaid inner shell, and wherein said check valve is operable to sealinglyengage said air dryer.
 18. The air dryer cartridge of claim 17, whereinsaid outlet of said inner shell comprises a plurality of holes, whereinsaid check valve comprises at least one flap moveable between a low flowrate position, in which said flap restricts the rate of flow of fluidthrough at least a portion of said holes, and a high flow rate position.19. The air dryer cartridge of claim 18, wherein said check valvecomprises a first seal portion coupled with and extending from saidflap, wherein said first seal portion seals between a portion of saidouter shell and a portion of said inner shell.
 20. The air dryercartridge of claim 19, wherein said check valve comprises a second sealportion coupled with and extending from said first seal portion, whereinsaid second seal portion is operable to sealingly engage said air dryer.